The Internet of Things (IoT) is the “Internet of connected objects”. Clients of the Internet of Things can be any object, and information exchange and communication can be performed therebetween. Such a communication manner is also referred to as machine type communication (MTC), and a communications node thereof is referred to as an MTC terminal. A typical Internet of Things application includes smart metering, smart household, and the like. The Internet of Things needs to be applied to a plurality of scenarios, for example, a plurality of environments such as indoors, outdoors, and underground. Therefore, many special requirements are imposed on a design of the Internet of Things.
First, the Internet of Things needs to have relatively strong coverage performance. Many MTC devices such as an electric meter and a water meter are located in an environment in which coverage is relatively poor. These MTC devices are usually installed in a place where a wireless network signal is very poor, such as a corner of a room or even a basement. In this case, a coverage enhancement technology is required to implement coverage of the Internet of Things.
Second, the Internet of Things needs to support a large quantity of low-rate devices. A quantity of MTC devices needs to be much greater than a quantity of devices used for inter-human communication. However, a data packet transmitted by the MTC device is very small, and the MTC device is insensitive to a delay.
Third, costs of the Internet of Things need to be very low. Many MTC applications require to obtain and use MTC devices at very low costs, so as to deploy the MTC devices in a large scale.
Fourth, an Internet of Things device needs to have a feature of low energy consumption. In most cases, an MTC device is powered by a battery. However, in many scenarios, the MTC device is required to be used for more than ten years without changing the battery. This requires that the MTC device can work at extremely low power consumption.
Until now, the expected objectives of low costs, large coverage, and low energy consumption still cannot be achieved. To satisfy the foregoing special requirements, in a recent NarrowBand Internet of Things (NB-IoT) subject, the following three operation modes are defined:                (1) Standalone operation: use an independent band, for example, one or more carriers in a Global System for Mobile Communications (GSM) network.        (2) In-band operation: use one or more physical resource blocks (PRB) in a Long Term Evolution (LTE) carrier.        (3) Guard-band operation: use a resource block that is not used in a guard band of an LTE carrier.        
Due to a limitation on bandwidth and resource allocation in an existing LTE system, when the NB-IoT is deployed in the in-band operation or the guard-band operation, a frequency resource matching an existing raster rule may not be found. Consequently, abase station and UE cannot communicate with each other normally. For example, when the NB-IoT is deployed in the in-band operation, an NB-IoT band and an LTE physical resource block (PRB) need be completely aligned. Due to existence of a downlink direct current subcarrier (DC subcarrier), a non-central LTE physical resource block cannot be found to satisfy the existing LTE raster rule.